1. Field of the Invention
The present invention relates to a pressure-applying fixing roller (hereinafter referred to as a “fixing pressure roller”) having an elastic layer formed of a porous elastomer such as a silicone porous elastomer, which fixing roller is suitably employed as a fixation roller, a pressure roller, or the like of a fixation unit.
2. Background Art
In electrophotographic image-forming apparatuses such as a printer and a copying machine, rollers such as a fixing roller and a pressure roller are employed in an image fixation unit for fixing an unfixed toner image. In operation, the fixing roller and the pressure roller in an image fixation unit are rotated at high temperature while the rollers are pressed to provide a nip portion. In order to reduce the energy required for heating the fixing pressure rollers, the heat capacity of the rollers must be reduced. One known means for this is employment of a porous member.
Conventionally, an elastic layer formed of silicone rubber foam produced by use of a foaming agent is employed. In such silicon rubber foam, the cell size and thickness of intercellular portion tend to vary, resulting in cell breakage at stress concentration when the rubber foam is compressed. In this case, the pressure of the nip portion lowers, causing unfavorable fixation failure.
Under such circumstances, a porous elastomer having spherical cells of a uniform size has become a promising material. The porous elastomer is produced from an emulsion composition having a continuous phase formed of a liquid rubber material which provides an elastomer through curing (see, for example, Patent Document 1).
However, when such a porous elastomer is bonded to a core metal shaft by use of a silane coupling agent, and the produced member is employed as an elastic layer of a fixing roller or a pressure roller in the fixation unit, a portion of the elastic layer in the vicinity of the core metal shaft is broken due to shear stress upon pressure application. In this case, transmission means such as driving force is problematically lost.    Patent Document 1: Japanese Patent No. 4638714